The program is concerned with developing animal models for biomedical research utilizing the VRB genetics resource by following the appropriate mating techniques. One component of the program involves forming, all on the same genetic background, four groups of mice which are defined with respect to T and B lymphocyte activity utilizing two independently occurring mutations; Nude (nu) which results in thymic dysgenesis and an X linked mutation which affects the maturation of B lymphocytes. This system is being established in 10 inbred mouse strains. Also, the mtuant called Motheaten (me) is being established in four inbred strains of mice and the gene named Dwarf (dw) in three strains. In the rats, the gene Corpulent (cp) is being established in two strains and the genes Diabetes Insipidus (di) and Jaundice (j) in two strains.